The invention relates to the detection of a drift or spread on injectors in relation to reference injectors in a common-rail fuel injection system.
The invention relates more specifically to a method for diagnosing a drift or spread on injectors belonging to a common-rail injection system.
A drift or spread means an abnormal delivery of fuel by at least one of the injectors of the injection system by comparison with a nominal delivery considered.
In present-day internal combustion engines, it has proven necessary and compulsory to fully master the quantities of fuel injected by the injection system in order to guarantee nominal engine operation. What happens is that any drift or spread on the injection of fuel by comparison with a nominal batch may have a significant impact on engine pollutant emissions and performance.
It is therefore essential to be able as soon as possible to detect any potential drift relating to the injectors of an injection system.
American patent application U.S. 2011/0030655 discloses a method that makes it possible to detect an abnormal injector delivery within an injection system. The injection system described in that application has a delivery regulating circuit comprising a delivery regulating value and a pressure regulating circuit. The method consists in detecting injection anomalies in the injection system when, with the delivery regulating circuit operating in closed loop and the pressure regulating circuit operating in open loop, the difference between a minimum throughflow of fuel through the delivery regulating value, which throughflow is established using a predetermined map that is a function of engine speed and the ordained injection quantity, and a throughflow of fuel established by the closed-loop control of the delivery regulating valve, is greater than a predetermined threshold value (K).
The method described in the aforementioned patent application does, however, have a certain number of drawbacks.
In particular, the method described allows a diagnosis to be reached only at certain operating points (stabilized points or specific points).
Moreover, because detection is based on just one single predetermined threshold value, it is necessary to plan for this value to be fairly high. As a result, only significant injector drifts can be detected.
In addition, the closed-loop value may drift as a result of drifts other than that affecting the injectors. Thus, the drift relating to the delivery may be associated with the sensor that measures the pressure of the fuel in the rail, with the high-pressure pump, with the discharge valve or even with any other factor that may cause the rail pressure or the delivery entering the common rail to vary. Now, the method described in the aforementioned application is unable to distinguish an injector drift from a drift caused by other components. In other words, with the method described in the American document, a drift may be observed even though the injectors are not drifting.